Effect of antiepileptic drugs on spontaneous seizures in epileptic rats

Fluvoxamine Ameliorates the Damage to the Neuro-Behavioral Status of Rats Caused by the Administration of Valproic Acid by Preventing Cognitive Memory Deficits and Decreased Hippocampal Cellular Proliferation

Fluvoxamine is a major antidepressant of the selective serotonin-reuptake inhibitor class, previously studied as a drug that improves cognitive memory by enhancing hippocampal cell division and proliferation. Valproic acid (VPA) is a commonly used antiepileptic drug and mood stabilizer that has negative effects on cognitive memory as it inhibits cellular division and proliferation in the hippocampus. This study assessed the protective effects of fluvoxamine treatment versus the memory impairment, decreased hippocampal cellular proliferation, and weight loss produced by VPA treatment. The cognitive memory of 40 male Sprague-Dawley rats was assessed by the novel object location (NOL) test. Immunostaining by Ki67 and glutathione peroxidase 1 (GPX-1) was performed to quantify the number of dividing cells in the subgranular zone (SGZ) of the dentate gyrus and to assess the antioxidant activity of different treatments, respectively. Results showed that the VPA group had fewer Ki67-positive cells than the control group (p < 0.001), indicating reduced hippocampal proliferation. In contrast, the VPA and fluvoxamine combination group showed increased proliferation (p < 0.001) compared to VPA alone. Notably, fluvoxamine treatment significantly differed in cell counts compared to other groups (p < 0.001). Fluvoxamine also attenuated the weight loss caused by VPA (p < 0.0001). Our data suggested that fluvoxamine therapy attenuated the VPA-induced decrease in SGZ cellular proliferation, memory, and weight in rats.

Chronic limbic epilepsy models for therapy discovery: Protocols to improve efficiency

OBJECTIVE

There have been recommendations to improve therapy discovery for epilepsy by incorporating chronic epilepsy models into the preclinical process, but unpredictable seizures and difficulties in maintaining drug levels over prolonged periods have been obstacles to using these animals. We report new protocols in which drugs are administered through a new chronic gastric tube to rats with higher seizure frequencies to minimize these obstacles.

METHODS

Adult rats with spontaneous limbic seizures following an episode of limbic status epilepticus induced by electrical hippocampal stimulation were monitored with long-term video- electroencephalography (EEG). Animals with a predetermined baseline seizure frequency received an intragastric tube for drug administration. Carbamazepine, levetiracetam, phenobarbital, and phenytoin were tested with either an acute protocol (an increasing single dose every other day for a maximum of three doses) or with a chronic protocol (multiple administrations of one dose for a week). Drug levels were obtained to correlate the effect with the level.

RESULTS

With the acute protocol, all four drugs induced a clear dose-related response. Similar dose-related responses were seen following the week-long dosing protocol for carbamazepine, phenobarbital, and phenytoin, and these responses were associated with drug levels that were in the human therapeutic range. The response to chronic levetiracetam was much less robust. The gastric tube route of administration was well tolerated over a number of months.

SIGNIFICANCE

Using rats with stable, higher seizure frequencies made it possible to identify the potential of a drug to suppress seizures in a realistic model of epilepsy with drug levels that are similar to those of human therapeutic levels. The acute protocol provided a full dose response in 1 week. The chronic administration protocol further differentiated drugs that may be effective long term. The gastric tube facilitates a less stressful, humane, and consistent administration of multiple doses.

Sensitivity of unilateral- versus bilateral-onset spike-wave discharges to ethosuximide and carbamazepine in the fluid percussion injury rat model of traumatic brain injury

Unilateral-onset spike-wave discharges (SWDs) following fluid percussion injury (FPI) in rats have been used for nearly two decades as a model for complex partial seizures in human posttraumatic epilepsy (PTE). This study determined if SWDs with a unilateral versus bilateral cortical onset differed. In this experiment, 2-mo-old rats received severe FPI (3 atm) or sham surgery and were instrumented for chronic video-electrocorticography (ECoG) recording (up to 9 mo). The antiseizure drug, carbamazepine (CBZ), and the antiabsence drug, ethosuximide (ETX), were administered separately to determine if they selectively suppressed unilateral- versus bilateral-onset SWDs, respectively. SWDs did not significantly differ between FPI and sham rats on any measured parameter (wave-shape, frequency spectrum, duration, or age-related progression), including unilateral (∼17%) versus bilateral (∼83%) onsets. SWDs with a unilateral onset preferentially originated ipsilateral to the craniotomy in both FPI and sham rats, suggesting that the unilateral-onset SWDs were related to surgical injury and not specifically to FPI. ETX profoundly suppressed SWDs with either unilateral or bilateral onsets, and CBZ had no effect on either type of SWD. These results suggest that SWDs with either a unilateral or bilateral onset have a pharmacosensitivity similar to absence seizures and are very different from the complex partial seizures of PTE. Therefore, SWDs with a unilateral onset after FPI are not a model of the complex partial seizures that occur in PTE, and their use for finding new treatments for PTE could be counterproductive, particularly if their close similarity to normal brain oscillations is not acknowledged.NEW & NOTEWORTHY Unilateral-onset spike-wave discharges (SWDs) in rats have been used to model complex partial seizures in human posttraumatic epilepsy (PTE), compared to bilateral-onset SWDs thought to reflect human absence seizures. Here, we show that both unilateral- and bilateral-onset SWDs following traumatic brain injury are suppressed by the antiabsence drug ethosuximide and are unaffected by the antiseizure drug carbamazepine. We propose that unilateral-onset SWDs are not useful for studying mechanisms of, or treatments for, PTE.

Effects of Lacosamide Treatment on Epileptogenesis, Neuronal Damage and Behavioral Comorbidities in a Rat Model of Temporal Lobe Epilepsy

Clinically, temporal lobe epilepsy (TLE) is the most prevalent type of partial epilepsy and often accompanied by various comorbidities. The present study aimed to evaluate the effects of chronic treatment with the antiepileptic drug (AED) lacosamide (LCM) on spontaneous motor seizures (SMS), behavioral comorbidities, oxidative stress, neuroinflammation, and neuronal damage in a model of TLE. Vehicle/LCM treatment (30 mg/kg, p.o.) was administered 3 h after the pilocarpine-induced status epilepticus (SE) and continued for up to 12 weeks in Wistar rats. Our study showed that LCM attenuated the number of SMS and corrected comorbid to epilepsy impaired motor activity, anxiety, memory, and alleviated depressive-like responses measured in the elevated plus maze, object recognition test, radial arm maze test, and sucrose preference test, respectively. This AED suppressed oxidative stress through increased superoxide dismutase activity and glutathione levels, and alleviated catalase activity and lipid peroxidation in the hippocampus. Lacosamide treatment after SE mitigated the increased levels of IL-1β and TNF-α in the hippocampus and exerted strong neuroprotection both in the dorsal and ventral hippocampus, basolateral amygdala, and partially in the piriform cortex. Our results suggest that the antioxidant, anti-inflammatory, and neuroprotective activity of LCM is an important prerequisite for its anticonvulsant and beneficial effects on SE-induced behavioral comorbidities.

Evaluation of subchronic administration of antiseizure drugs in spontaneously seizing rats

OBJECTIVE

Approximately 30% of patients with epilepsy do not experience full seizure control on their antiseizure drug (ASD) regimen. Historically, screening for novel ASDs has relied on evaluating efficacy following a single administration of a test compound in either acute electrical or chemical seizure induction. However, the use of animal models of spontaneous seizures and repeated administration of test compounds may better differentiate novel compounds. Therefore, this approach has been instituted as part of the National Institute of Neurological Disorders and Stroke Epilepsy Therapy Screening Program screening paradigm for pharmacoresistant epilepsy.

METHODS

Rats were treated with intraperitoneal kainic acid to induce status epilepticus and subsequent spontaneous recurrent seizures. After 12 weeks, rats were enrolled in drug screening studies. Using a 2-week crossover design, selected ASDs were evaluated for their ability to protect against spontaneous seizures, using a video-electroencephalographic monitoring system and automated seizure detection. Sixteen clinically available compounds were administered at maximally tolerated doses in this model. Dose intervals (1-3 treatments/d) were selected based on known half-lives for each compound.

RESULTS

Carbamazepine (90 mg/kg/d), phenobarbital (30 mg/kg/d), and ezogabine (15 mg/kg/d) significantly reduced seizure burden at the doses evaluated. In addition, a dose-response study of topiramate (20-600 mg/kg/d) demonstrated that this compound reduced seizure burden at both therapeutic and supratherapeutic doses. However, none of the 16 ASDs conferred complete seizure freedom during the testing period at the doses tested.

SIGNIFICANCE

Despite reductions in seizure burden, the lack of full seizure freedom for any ASD tested suggests that this screening paradigm may be useful for testing novel compounds with potential utility in pharmacoresistant epilepsy.

Valproic Acid and Epilepsy: From Molecular Mechanisms to Clinical Evidences

After more than a century from its discovery, valproic acid (VPA) still represents one of the most efficient antiepi-leptic drugs (AEDs). Pre and post-synaptic effects of VPA depend on a very broad spectrum of actions, including the regu-lation of ionic currents and the facilitation of GABAergic over glutamatergic transmission. As a result, VPA indirectly mod-ulates neurotransmitter release and strengthens the threshold for seizure activity. However, even though participating to the anticonvulsant action, such mechanisms seem to have minor impact on epileptogenesis. Nonetheless, VPA has been reported to exert anti-epileptogenic effects. Epigenetic mechanisms, including histone deacetylases (HDACs), BDNF and GDNF modulation are pivotal to orientate neurons toward a neuroprotective status and promote dendritic spines organization. From such broad spectrum of actions comes constantly enlarging indications for VPA. It represents a drug of choice in child and adult with epilepsy, with either general or focal seizures, and is a consistent and safe IV option in generalized convulsive sta-tus epilepticus. Moreover, since VPA modulates DNA transcription through HDACs, recent evidences point to its use as an anti-nociceptive in migraine prophylaxis, and, even more interestingly, as a positive modulator of chemotherapy in cancer treatment. Furthermore, VPA-induced neuroprotection is under investigation for benefit in stroke and traumatic brain injury. Hence, VPA has still got its place in epilepsy, and yet deserves attention for its use far beyond neurological diseases. In this review, we aim to highlight, with a translational intent, the molecular basis and the clinical indications of VPA.

Valproic acid withdrawal ameliorates impairments of hippocampal-spatial working memory and neurogenesis

Valproic acid (VPA), an agent that is used to treat epileptic seizures, can cause spatial memory impairment in adults and children. This effect is thought to be due to the ability of VPA to inhibit neurogenesis in the hippocampus, which is required for learning. We have previously used an animal model to show that VPA significantly impairs hippocampal-spatial working memory and inhibits neuronal generation in the sub-granular zone of the dentate gyrus. As there are patient reports of improvements in memory after discontinuing VPA treatment, the present study investigated the recovery of both spatial memory and hippocampal neurogenesis at two time points after withdrawal of VPA. Male Wistar rats were given intraperitoneal injections of 0.9% normal saline or VPA (300 mg/kg) twice a day for 10 d. At 1, 30, or 45 d after the drug treatment, the novel object location (NOL) test was used to examine spatial memory; hippocampal cell division was counted using Ki67 immunohistochemistry, and levels of brain-derived neurotrophic factor (BDNF) and Notch1 were measured using western immunoblotting. Spatial working memory was impaired 1 and 30 d after the final administration, but was restored to control levels by 45 d. Cell proliferation had increased to control levels at 30 and 45 d. Both markers of neurogenesis (BDNF and Notch1 levels) had returned to control levels at 45 d. These results demonstrate that memory recovery occurs over a period of six weeks after discontinuing VPA treatment and is preceded by a return of hippocampal neurogenesis to control levels.

Effect of carbamazepine on spontaneous recurrent seizures recorded from the dentate gyrus in rats with kainate-induced epilepsy

OBJECTIVE

Animal models of chronic epilepsy with spontaneous recurrent seizures (SRSs) may be useful in the discovery and mechanistic analyses of antiseizure drugs (ASDs). Carbamazepine (CBZ), a widely used ASD with a well-defined mechanism, was analyzed in this proof-of-principle study to determine how a traditional ASD affects the properties of SRSs.

METHODS

The effects of CBZ on electrographic SRSs recorded from the dentate gyrus were studied in freely behaving rats using a repeated, low-dose kainate model of acquired epilepsy with a repeated-measures, crossover protocol.

RESULTS

Almost all seizure durations were >20 seconds. Both seizure likelihood and duration appeared to be similar between 1 and 8 hours after individual CBZ injections. CBZ-induced decreases in seizure frequency were not significant at 10 mg/kg; however, at 30 mg/kg, seizure frequency was significantly reduced for convulsive but not nonconvulsive seizures. At 100 mg/kg, CBZ strongly suppressed both convulsive and nonconvulsive seizures. Although CBZ had a dose-dependent effect on seizure frequency, CBZ did not affect seizure duration at any dose. The preceding interictal interval did not affect seizure duration; however, at 30 mg/kg CBZ, nearly all seizures were nonconvulsive when the interictal interval was <30 minutes (ie, during clusters).

SIGNIFICANCE

Increased doses of CBZ (10-100 mg/kg) suppressed the frequency but not the duration of convulsive and nonconvulsive seizures in the repeated, low-dose kainate model. The repeated-measures, crossover protocol, which requires relatively few animals and compensates for progressive increases in seizure frequency during epileptogenesis after status epilepticus, allowed quantitative analyses of clinically relevant and translatable properties of SRSs.

A Mesiotemporal Lobe Epilepsy Mouse Model

Among the different forms of epilepsies, mesiotemporal lobe epilepsy (MTLE) is one of the most common and represents the main pharmaco-resistant form of epilepsy. There is therefore an urgent need to better understand this form of epilepsy to develop better anti-epileptic drugs. Many rodent models are mimicking some aspects of the human temporal lobe epilepsy but only few are addressing most of the human mesiotemporal lobe epilepsy. In this article, we describe the main characteristics of a mouse of model of mesial temporal lobe epilepsy. This model is generated by a single injection of kainic acid into the dorsal hippocampus which reproduces most of the morphological and electrophysiological features of human MTLE in a mouse. This model may help to better understand mesial temporal lobe epilepsy and the development of new therapeutic drugs.

Fluoxetine prevents the memory deficits and reduction in hippocampal cell proliferation caused by valproic acid

Valproic acid (VPA), a commonly used antiepileptic drug, has been reported to cause cognitive impairments in patients. In a previous study, using a rodent model, we showed that VPA treatment impaired cognition which was associated with a reduction in the cell proliferation required for hippocampal neurogenesis. The antidepressant fluoxetine has been shown to increase hippocampal neurogenesis and to reverse the memory deficits found in a number of pathological conditions. In the present study we investigated the protective effects of fluoxetine treatment against the impairments in memory and hippocampal cell proliferation produced by VPA. Male Sprague Dawley rats received daily treatment with fluoxetine (10mg/kg) by oral gavage for 21days. Some rats were co-administered with VPA (300mg/kg, twice daily i.p. injections) for 14days from day 8 to day 21 of the fluoxetine treatment. Spatial memory was tested using the novel object location (NOL) test. The number of proliferating cells present in the sub granular zone of the dentate gyrus was quantified using Ki67 immunohistochemistry at the end of the experiment. Levels of the receptor Notch1, the neurotrophic factor BDNF and the neural differentiation marker DCX were determined by Western blotting. VPA-treated rats showed memory deficits, a decrease in the number of proliferating cells in the sub granular zone and decreases in the levels of Notch1 and BDNF but not DCX compared to control animals. These changes in behavior, cell proliferation and Notch1 and BDNF were prevented in animals which had received both VPA and fluoxetine. Rats receiving fluoxetine alone did not show a significant difference in the number of proliferating cells or behavior compared to controls. These results demonstrated that the spatial memory deficits and reduction of cell proliferation produced by VPA can be ameliorated by the simultaneous administration of the antidepressant fluoxetine.

Seizures triggered by pentylenetetrazol in marmosets made chronically epileptic with pilocarpine show greater refractoriness to treatment

The efficiency of most of the new antiepileptic drugs (AEDs) on clinical trials still falls short the success reported in pre-clinical studies, possibly because the validity of the animal models is insufficient to fully represent the human pathology. To improve the translational value for testing AEDs, we propose the use of non-human primates. Here, we suggest that triggering limbic seizures with low doses of PTZ in pilocarpine-treated marmosets might provide a more effective basis for the development of AED. Marmosets with epileptic background were more susceptible to seizures induced by PTZ, which were at least 3 times longer and more severe (about 6 times greater frequency of generalized seizures) in comparison to naïve peers. Accordingly, PTZ-induced seizures were remarkably less attenuated by AEDs in epileptic than naïve marmosets. While phenobarbital (40mg/kg) virtually abolished seizures regardless of the animal's background, carbamazepine (120mg/kg) and valproic acid (400mg/kg) could not prevent PTZ-induced seizures in epileptic animals with the same efficiency as observed in naïve peers. VPA was less effective regarding the duration of individual seizures in epileptic animals, as assessed in ECoG (p=0.05). Similarly following CBZ treatment, the behavioral manifestation of generalized seizures lasted longer in epileptic (p<0.05), which were also more frequent than in the naïve group (p<0.05). As expected, epileptic marmosets experiencing stronger seizures showed more NPY- and ΔFosB-immunostained neurons in a number of brain areas associated with the generation and spread of limbic seizures. Our results suggest that PTZ induced seizures over an already existing epileptic background constitutes a reliable and controllable mean for the screening of new AEDs.

Vigabatrin therapy implicates neocortical high frequency oscillations in an animal model of infantile spasms

Abnormal high frequency oscillations (HFOs) in EEG recordings are thought to be reflections of mechanisms responsible for focal seizure generation in the temporal lobe and neocortex. HFOs have also been recorded in patients and animal models of infantile spasms. If HFOs are important contributors to infantile spasms then anticonvulsant drugs that suppress these seizures should decrease the occurrence of HFOs. In experiments reported here, we used long-term video/EEG recordings with digital sampling rates capable of capturing HFOs. We tested the effectiveness of vigabatrin (VGB) in the TTX animal model of infantile spasms. VGB was found to be quite effective in suppressing spasms. In 3 of 5 animals, spasms ceased after a daily two week treatment. In the other 2 rats, spasm frequency dramatically decreased but gradually increased following treatment cessation. In all animals, hypsarrhythmia was abolished by the last treatment day. As VGB suppressed the frequency of spasms, there was a decrease in the intensity of the behavioral spasms and the duration of the ictal EEG event. Analysis showed that there was a burst of high frequency activity at ictal onset, followed by a later burst of HFOs. VGB was found to selectively suppress the late HFOs of ictal complexes. VGB also suppressed abnormal HFOs recorded during the interictal periods. Thus VGB was found to be effective in suppressing both the generation of spasms and hypsarrhythmia in the TTX model. Vigabatrin also appears to preferentially suppress the generation of abnormal HFOs, thus implicating neocortical HFOs in the infantile spasms disease state.

Ethosuximide reduces electrographical and behavioral correlates of alcohol withdrawal seizure in DBA/2J mice

Chronic alcohol abuse depresses the nervous system and, upon cessation, rebound hyperexcitability can result in withdrawal seizure. Withdrawal symptoms, including seizures, may drive individuals to relapse, thus representing a significant barrier to recovery. Our lab previously identified an upregulation of the thalamic T-type calcium (T channel) isoform CaV3.2 as a potential contributor to the generation and propagation of seizures in a model of withdrawal. In the present study, we examined whether ethosuximide (ETX), a T-channel antagonist, could decrease the severity of ethanol withdrawal seizures by evaluating electrographical and behavioral correlates of seizure activity. DBA/2J mice were exposed to an intermittent ethanol exposure paradigm. Mice were treated with saline or ETX in each withdrawal period, and cortical EEG activity was recorded to determine seizure severity. We observed a progression in seizure activity with each successive withdrawal period. Treatment with ETX reduced ethanol withdrawal-induced spike and wave discharges (SWDs), in terms of absolute number, duration of events, and contribution to EEG power in the 6-10 Hz frequency range. We also evaluated the effects of ETX on handling-induced convulsions. Overall, we observed a decrease in handling-induced convulsion severity in mice treated with ETX. Our findings suggest that ETX may be a useful pharmacological agent for studies of alcohol withdrawal and treatment of resulting seizures.

The intrahippocampal kainate model of temporal lobe epilepsy revisited: epileptogenesis, behavioral and cognitive alterations, pharmacological response, and hippoccampal damage in epileptic rats

Systemic or intracerebral (e.g., intrahippocampal or intraamygdalar) administration of kainate, a potent neurotoxic analog of glutamate, is widely used to induce status epilepticus (SE) and subsequent development of epilepsy in rats. However, in apparent contrast to systemic administration, following intracerebral injection the proportion of rats that have been observed to generate spontaneous recurrent seizures (SRS) and the frequency of the SRS are comparatively low. More recently, it has been shown that these problems can be resolved by injecting kainate into the dorsal hippocampus of awake rats, thus avoiding the insult-modifying effects of anesthesia, which had often been used for intracerebral injection of this convulsant in previous studies. For further characterization of this model, we injected kainate (0.4 μg) unilaterally into the CA3 of the posterior hippocampus in awake rats, which induced limbic SE (ranging from 4 to 20 h) in all rats without mortality. Repeated video-EEG monitoring (24h/day, 7 days/week) for periods of 1-2.5 weeks from 1 to 8 months after SE demonstrated that 91% of the rats developed epilepsy, and that seizure frequency significantly increased over the course of the disease. Epilepsy was associated with increased behavioral excitability and impaired learning and memory in a water maze, most likely as a result of hippocampal pathology, which was characterized by extensive neuronal loss in CA3 and dentate hilus and dispersion of granule cells in the ipsilateral hippocampus. A drug trial with phenobarbital showed that all epileptic rats used in this trial responded to treatment with suppression of SRS. The data substantiate that intrahippocampal kainate injection in awake rats offers an excellent model of human temporal lobe epilepsy and indicate that this model may have particular advantages for studying mechanisms of injury-induced epilepsy and comorbidities as targets for antiepileptic and antiepileptogenic therapies.

Carbamazepine, but not valproate, displays pharmacoresistance in lamotrigine-resistant amygdala kindled rats

The voltage gated sodium channel (VGSC) blocker lamotrigine (LTG), when administered during kindling acquisition, leads to the development of resistance to LTG. The present study aimed to assess whether LTG-resistant amygdala-kindled rats display subsequent resistance to the VGSC blocker carbamazepine (CBZ) and the broad-spectrum antiepileptic drug (AED) sodium valproate (VPA). Two groups of male Sprague Dawley rats received either 0.5% methylcellulose (MC) or LTG (5mg/kg, i.p.) 1h before each amygdala kindling stimulation. Treatments were stopped once both the groups were fully kindled. Two days later, both groups were challenged with a higher dose of LTG (15mg/kg, i.p.) to verify LTG-resistance in the experimental group (i.e., LTG-pretreated rats). The efficacy of CBZ and VPA was then evaluated in both groups. A higher dose of LTG blocked fully kindled seizures in the vehicle-treated rats but not seizures in the LTG-treated group. The mean seizure score, of the control group (1.2±0.3) was significantly lower (P<.05) than that of the LTG-treated population (3.5±0.7; n=8). A lower percent of the population in the control group was observed to display a generalized stage 4-5 seizure compared to the experimental group (i.e., those that received LTG during kindling acquisition) (28.5% vs. 62%, respectively). Interestingly, CBZ (10, 20, and 40mg/kg) displayed a dose-dependent anticonvulsant effect in the vehicle-kindled group, but was less effective in LTG-treated animals. In contrast, VPA (300mg/kg) effectively blocked the behavioral seizure and decreased the afterdischarge duration (ADD) in both vehicle and LTG groups. These findings suggest that the LTG-resistant, amygdala-kindled rat may represent a novel model of pharmacoresistant epilepsy.

The antidepressants citalopram and reboxetine reduce seizure frequency in rats with chronic epilepsy

PURPOSE

  For a long time, antidepressants have been thought to possess proconvulsant properties. This assumption, however, remains controversial, since anticonvulsant effects have been attributed to certain antidepressants. To date, it remains unclear which antidepressants can be used for the treatment of depression in patients with epilepsy. In this respect, studies investigating the convulsant liability of antidepressants in a chronic epilepsy model can give valuable information. The present study was designed to determine the seizure liability of citalopram and reboxetine in the kainic acid-induced post-status epilepticus model for temporal lobe epilepsy.

METHODS

  Two months after the induction of status epilepticus, chronic epileptic rats (n = 16) were video-electroencephalography (EEG) monitored during seven consecutive weeks. Weeks 1, 3, 5, and 7 served as sham weeks during which the rats received intraperitoneal saline injections for four consecutive days, followed by a 3-day sham washout period during which no injections were given. During weeks 2, 4, and 6, rats received intraperitoneal injections with either citalopram (5, 10, and 15 mg/kg, once daily, n = 8) or reboxetine (10, 20, and 30 mg/kg, twice daily, n = 8) for 4 days, again followed by a washout period of 3 days. Drugs were administered in a randomly assigned fixed-dose regimen per week. Each rat served as its own control. The drug doses were selected based on the doses reported to have antidepressant effects in rats.

KEY FINDINGS

  Citalopram significantly decreased the spontaneous seizure frequency at the highest dose tested, that is, the mean number of seizures decreased from 12.8 seizures to 8.8 seizures per week (31%) after treatment with 15 mg/kg citalopram. This dose also significantly decreased the cumulative seizure duration. Administration of 5 and 10 mg/kg citalopram did not alter the seizure frequency. The two highest doses of reboxetine significantly decreased the spontaneous seizure frequency, that is, 20 mg/kg reboxetine decreased the seizure frequency from 14.1 to 7.9 (44%) and 30 mg/kg reboxetine decreased the seizure frequency from 11.8 to 7.2 (39%). In addition, both doses significantly decreased the cumulative seizure duration. Administration of 10 mg/kg reboxetine did not alter seizure frequency. Citalopram and reboxetine had no effect on seizure severity and seizure duration in any of the doses tested.

SIGNIFICANCE

  In general we can conclude that antidepressant doses of citalopram and reboxetine have, depending on the dose, an anticonvulsant effect or no effect on spontaneous seizures in the kainic acid-induced post-status epilepticus rat model.

Low frequency stimulation of ventral hippocampal commissures reduces seizures in a rat model of chronic temporal lobe epilepsy

PURPOSE

To investigate the effects of low frequency stimulation (LFS) of a fiber tract for the suppression of spontaneous seizures in a rat model of human temporal lobe epilepsy.

METHODS

Stimulation electrodes were implanted into the ventral hippocampal commissure (VHC) in a rat post-status epilepticus (SE) model of human temporal lobe epilepsy (n = 7). Two recording electrodes were placed in the CA3 regions bilaterally and neural data were recorded for a minimum of 6 weeks. LFS (60 min train of 1 Hz biphasic square wave pulses, each 0.1 ms in duration and 200 μA in amplitude, followed by 15 min of rest) was applied to the VHC for 2 weeks, 24 h a day.

KEY FINDINGS

The baseline mean seizure frequency of the study animals was 3.7 seizures per day. The seizures were significantly reduced by the application of LFS in every animal (n = 7). By the end of the 2-week period of stimulation, there was a significant, 90% (<1 seizure/day) reduction of seizure frequencies (p < 0.05) and a 57% reduction during the period following LFS (p < 0.05) when compared to baseline. LFS also resulted in a significant reduction of hippocampal interictal spike frequency (71%, p < 0.05), during 2 weeks of LFS session. The hippocampal histologic analysis showed no significant difference between rats that received LFS and SE induction and those that had received only SE-induction. None of the animals showed any symptomatic hemorrhage, infection, or complication.

SIGNIFICANCE

Low frequency stimulation applied at a frequency of 1 Hz significantly reduced both the excitability of the neural tissue as well as the seizure frequency in a rat model of human temporal lobe epilepsy. The results support the hypothesis that LFS of fiber tracts can be an effective method for the suppression of spontaneous seizures in a temporal lobe model of epilepsy in rats and could lead to the development of a new therapeutic modality for human patients with temporal lobe epilepsy.

Valproic acid improves locomotion in vivo after SCI and axonal growth of neurons in vitro

Previous studies have found that valproic acid (VPA), a histone deacetylases (HDAC) inhibitor, improves outcomes in a rat model of spinal cord injury (SCI). The study here aimed to further illuminate the neuroprotective effects of VPA against SCI, both in vivo and in vitro. First, spinal cord injury was performed in rats using NYU impactor. Delayed VPA injection (8 h following SCI) significantly accelerated locomotor recovery. VPA therapy also suppressed SCI-induced hypoacetylation of histone and promoted expressions of BDNF and GDNF. Next, the influence of VPA on axonal growth inhibited by a myelin protein was tested. Neurons from embryonic spinal cord or hippocampus were cultured on plates coated with Nogo-A peptide, and escalating concentrations of VPA were added into the cultures. VPA treatment, in a concentration dependent manner, allowed neurons to overcome Nogo-A inhibition of neurite outgrowth. Meanwhile, VPA exposure increased the level of histone acetylation and expression of BDNF in spinal neurons. Cumulatively, these findings indicate that VPA is possibly a promising medication and deserves translational trials for spinal cord injury.

The best model for a cat is the same cat...or is it?

Effect of Antiepileptic Drugs on Spontaneous Seizures in Epileptic Rats. Nissinen J, Pitkänen A. Epilepsy Res 2007;73:181–191. The present study investigated whether spontaneously seizing animals are a valid model for evaluating antiepileptic compounds in the treatment of human epilepsy. We examined whether clinically effective antiepileptic drugs (AEDs), including carbamazepine (CBZ), valproic acid (VPA), ethosuximide (ESM), lamotrigine (LTG), or vigabatrin (VGB) suppress spontaneous seizures in a rat model of human temporal lobe epilepsy, in which epilepsy is triggered by status epilepticus induced by electrical stimulation of the amygdala. Eight adult male rats with newly diagnosed epilepsy and focal onset seizures were included in the study. Baseline seizure frequency was determined by continuous video-electroencephalography (EEG) monitoring during a 7 days baseline period. This was followed by a 2–3 days titration period, a 5–7 days treatment period, and a 2–3 days wash-out period. During the 5–7 days treatment period, animals were treated successively with CBZ (120mg/kg/day), VPA (600mg/kg/day), ESM (400mg/kg/day), LTG (20mg/kg/day), and VGB (250mg/kg/day). VPA, LTG, and VGB were the most efficient of the compounds investigated, decreasing the mean seizure frequency by 83, 84, and 60%, respectively. In the VPA group, the percentage of rats with a greater than 50% decrease in seizure frequency was 100%, in the LTG group 88%, in the VGB group 83%, in the CBZ group 29%, and in the ESM group 38%. During the 7 day treatment period, 20% of the VPA-treated animals and 14% of the CBZ-treated animals became seizure-free. These findings indicate that rats with focal onset spontaneous seizures respond to the same AEDs as patients with focal onset seizures. Like in humans, the response to AEDs can vary substantially between animals. These observations support the idea that spontaneously seizing animals are a useful tool for testing novel compounds for the treatment of human epilepsy.

ECoG studies of valproate, carbamazepine and halothane in frontal-lobe epilepsy induced by head injury in the rat

The use of electrocorticography (ECoG) with etiologically realistic epilepsy models promises to facilitate the discovery of better anti-epileptic drugs (AEDs). However, this novel approach is labor intensive, and must be optimized. To this end, we employed rostral parasagittal fluid percussion injury (rpFPI) in the adolescent rat, which closely replicates human contusive closed head injury and results in posttraumatic epilepsy (PTE). We systematically examined variables affecting the power to detect anti-epileptic effects by ECoG and used a non-parametric bootstrap strategy to test several different statistics, study designs, statistical tests, and impact of non-responders. We found that logarithmically transformed data acquired in repeated-measures experiments provided the greatest statistical power to detect decreases in seizure frequencies of preclinical interest with just 8 subjects and with up to approximately 40% non-responders. We then used this optimized design to study the anti-epileptic effects of acute exposure to halothane, and chronic (1 week) exposures to carbamazepine (CBZ) and valproate (VPA) 1 month post-injury. While CBZ was ineffective in all animals, VPA induced, during treatment, a progressive decrease in seizure frequency in animals primarily suffering from non-spreading neocortical seizures, but was ineffective in animals with a high frequency of spreading seizures. Halothane powerfully blocked all seizure activity. The data show that rpFPI and chronic ECoG can conveniently be employed for the evaluation of AEDs, suggest that VPA may be more effective than CBZ to treat some forms of PTE, and support the theory that pharmacoresistance may depend on the severity of epilepsy. The data also demonstrate the utility of chronic exposures to experimental drugs in preclinical studies and highlight the need for greater attention to etiology in clinical studies of AEDs.

Valproic acid reduces spatial working memory and cell proliferation in the hippocampus

Valproic acid (VPA) is widely used clinically, as an anticonvulsant and mood stabilizer but is, however, also known to block cell proliferation through its ability to inhibit histone deacetylase enzymes. There have been a number of reports of cognitive impairments in patients taking VPA. In this investigation we examined the relationship between cognition and changes in cell proliferation within the hippocampus, a brain region where continued formation of new neurons is associated with learning and memory. Treatment of rats by i.p. injection of VPA, reduced cell proliferation in the sub granular zone of the dentate gyrus within the hippocampus. This was linked to a significant impairment in their ability to perform a hippocampus-dependent spatial memory test (novel object location). In addition, drug treatment caused a significant reduction in brain-derived neurotrophic factor (BDNF) and Notch 1 but not doublecortin levels within the hippocampus. These results support the idea that VPA may cause cognitive impairment and provide a possible mechanism for this by reducing neurogenesis within the hippocampus.

Effects of lamotrigine and topiramate on hippocampal neurogenesis in experimental temporal-lobe epilepsy

Lamotrigine (LTG) and topiramate (TPM), two of the most commonly used new-generation antiepileptic drugs (AEDs), have been shown to produce no adverse and impaired cognitive effects in patients with epilepsy, respectively. As seizure-induced neurogenesis might contribute to cognitive deficits that are associated with status epilepticus (SE), we examined whether these two drugs produce differential effects on seizure-induced neurogenesis in the hippocampus of adult rats. Lithium pilocarpine model was used to mimic human temporal-lobe epilepsy. Five hours after SE, LTG and TPM were administered intragastrically twice daily throughout the entire length of the experiment with total daily dose of 20 and 80 mg/kg, respectively. The hippocampal neurogenesis was examined using 5-bromodeoxyuridine and doublecortin immunohistochemistry. Both LTG and TPM treatments significantly inhibited seizure-induced proliferation of neural progenitors in the hippocampus, but did not affect the neuronal differentiation of newborn cells. Long-term treatment with both AEDs decreased the number of spontaneous recurrent seizures after SE and alleviated chronic seizure-induced neuronal injury in the dentate hilus. Eventually, TPM significantly increased the number of newborn neurons in the dentate granular cell layer after seizures likely by promoting the survival of newborn neurons. In contrast, LTG treatment significantly reduced the number of ectopic hilar newborn neurons after seizures. Neither of them prevented the formation of hilar basal dendrites of newborn neurons in the epileptic hippocampus. These results indicate that TPM but not LTG promotes aberrant neuron regeneration in the hippocampus after SE, which might be partially related to their differential effects on cognitive function.

Antiepileptogenic and antiictogenic effects of retigabine under conditions of rapid kindling: an ontogenic study

PURPOSE

To examine antiepileptogenic and antiictogenic potential of retigabine (RTG) under conditions of rapid kindling epileptogenesis during different stages of development.

METHODS

The experiments were performed in postnatal day 14 (P14), P21, and P35 male Wistar rats. After stereotaxic implantation of hippocampal stimulating and recording electrodes, the effects of RTG on baseline afterdischarge (AD) properties were studied. Next, the animals underwent rapid kindling (sixty 10 s trains, bipolar 20 Hz square wave pulses delivered every 5 min). The progression of seizures (kindling acquisition), and responses to test stimulations after kindling (retention) were compared between RTG and vehicle-treated rats. Additionally, the effects of RTG on the severity of seizures in previously kindled animals were examined.

RESULTS

When administered intraperitoneally in doses that induced only mild, or no motor deficits, RTG significantly dampened brain excitability, evident as the increase of AD threshold and shortening of AD duration. During kindling, RTG delayed the development of focal seizures in P14 rats, and prevented the occurrence of full limbic seizures at all three ages. At P14 and P21, but not at P35, pretreatment with RTG prevented the establishment of kindling-induced enhanced seizure susceptibility. Administration of RTG to kindled animals decreased the severity of seizures induced by test stimulation. The effect was most prominent at P14.

DISCUSSION

RTG exerted both antiepileptogenic and antiictogenic effects under conditions of rapid kindling model. These effects were apparent during postneonatal, early childhood, and adolescent stages of development.